This project is directed towards understanding the relationship between dopamine (DA) and higher cognitive function, including working memory (WM) and executive control. The effects of DA agonists on tasks that depend on these higher cognitive functions will be explored in healthy human subjects with varying degrees of WM capacity. The relationship between dopamine and WM is complex, with the effects of DA agonists depending on baseline WM capacity. This relationship will be investigated using functional magnetic resonance imaging (fMRI) in healthy young individuals after the administration of a dopamine agonist to study the role of DA in cognitive efficiency and top-down modulation. As part of a larger study, positron emission tomography (PET) neurochemical imaging will also be utilized to study pharmacological mechanisms underlying these effects of DA on cognition. DA is of fundamental importance to the etiology of a wide variety of neurobehavioral disorders such as Parkinson's disease, attention deficit hyperactivity disorder, schizophrenia and drug addiction. A further understanding of the relationship between DA and cognition should advance our understanding of the mechanisms underlying cognitive and behavioral deficits in these disorders and provide insight into novel approaches to treating such deficits with medications targeted at specific neurotransmitter systems.